Device for Pulling a Trailer and/or Retaining a Load Carrying Unit

ABSTRACT

In order to improve a device for pulling a trailer and/or retaining a load carrying unit that is mountable at the rear end of a motor vehicle body and which comprises a supporting arm that is connected by a first end region to the motor vehicle body and is provided at a second end region with an element for attaching the trailer and/or for fixing the load carrying unit and furthermore which comprises sensors for capturing reversible deformations of the supporting arm caused by loads on the supporting arm in such a manner as to provided a device with which an allocation of captured elongations to individual applications of force is possible in as simple a way as possible, it is proposed that strain sensors which are affected by reversible deformations thereof be assigned to a supporting arm section of the supporting arm, and that, for capturing at least one selected bending strain, at least one strain sensor be arranged on one side and at least one strain sensor on an opposite side of a surface region of a neutral reference surface assigned to the selected bending load and that each of the strain sensors be arranged at a distance from this surface region.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application is a continuation of International application numberPCT/EP2017/060563 filed on May 3, 2017.

This patent application claims the benefit of International applicationNo. PCT/EP2017/060563 of May 3, 2017 and German application No. 10 2016108 541.3 of May 9, 2016, the teachings and disclosure of which arehereby incorporated in their entirety by reference thereto.

BACKGROUND OF THE INVENTION

The invention relates to a device for pulling a trailer and/or retaininga load carrying unit which is mountable at the rear end of a motorvehicle body and comprises a supporting arm that is connected to themotor vehicle body by a first end region and is provided at a second endregion thereof with an element for attaching the trailer and/or forfixing the load carrying unit, and furthermore comprising sensors fordetecting reversible deformations of the supporting arm caused by loadson the supporting arm.

A device of this type is known from DE 10 2014 013 812 A1 for example.

In the case of this device however, it is not possible to assign theelongations captured by a plurality of sensors located at differentpositions of the supporting arm to the individually applied forces in asimple manner.

Consequently, the object of the invention is to provide a device inwhich it is possible to allocate captured elongations to individuallyapplied forces in as simple a manner as possible.

SUMMARY OF THE INVENTION

In accordance with the invention, this object is achieved in a device ofthe type described hereinabove in that strain sensors which are affectedby reversible deformations thereof are assigned to a supporting armsection of the supporting arm, and in that, for capturing at least oneselected bending load, at least one strain sensor is arranged on oneside and at least one strain sensor is arranged on an opposite side of asurface region of a neutral reference surface assigned to the selectedbending load and in that the strain sensors are each arranged at adistance from this surface region.

The distance of the respective strain sensor from the surface region isat least 2 mm, more preferably at least 4 mm, preferably at least 6 mmfor example.

The advantage of the solution in accordance with the invention is thusto be seen in that, due to the arrangement of at least one strain sensoron mutually opposite sides of the surface region of the neutralreference surface, it is possible to capture the selected elongation inthat the strain sensors arranged on the different sides of the neutralreference surface capture elongations of different prefix sign, i.e.once in the form of an elongation and once as a compressive distortionand thus the contribution of the bending load to the elongationsmeasured by the strain sensors can be more simply determined.

Furthermore, it is particularly advantageous that the strain sensors arelocated on differing mutually opposite sides of a surface region of theneutral reference surface, i.e. a partial surface area of the neutralreference surface, so that the strain sensors thereby capture thereversible deformations implemented by the same volume region of thesupporting arm in one instance as an elongation and then as acompressive distortion.

In one solution in accordance with the invention, a neutral referencesurface is to be understood as being that surface which, on the onehand, runs through the neutral axis in the supporting arm that is formedin the case of the selected bending load, and which on the other handextends transversely to a bending movement surface.

Hereby, a bending movement surface in the sense of the solution inaccordance with the invention is to be understood as being that surfaceparallel to which the supporting arm moves with the smallest amount oftransverse movement relative to this surface in the event of a bendingload triggered by an application of force in a single defined directionand which runs through the neutral axis of the supporting arm thatensues in the case of this bending load.

In accord with an approximation, the bending movement surface runsparallel to the direction in which the force is applied and through therespective neutral axis.

Furthermore, as a rough approximation, the vertical bending movementsurface in the case of a curved supporting arm is a surface runningcentrally through every section of the supporting arm and approximatelyparallel to the direction of the vertical application of force.

An approximately parallel path is to be understand in particular asbeing a path which deviates from an exactly parallel path by up to amaximum of ±30° but more preferably maximally ±20°.

If it is necessary within the framework of the device in accordance withthe invention to capture a plurality of bending loads, then a neutralreference surface is assigned to each bending load.

In particular, there is provided in the context of the solution inaccordance with the invention to subject the supporting arm to avertical bending load and a transverse bending load, whereby in the caseof a vertical bending load a vertical neutral reference surface isformed and in the case of a transverse bending load a transverse neutralreference surface is formed.

Up to now, no particular details in regard to the surface region of therespective neutral reference surface and the relative arrangement of thestrain sensors to this surface region have been given.

Thus, it is expedient if a vertical projection of the strain sensorsthat are arranged on mutually opposite sides of the neutral referencesurface onto the surface region lies within this surface region. That isto say, that the projection of each of the strain sensors onto thissurface region lies within it.

Furthermore, the position of the strain sensors relative to each otheris given yet more precisely in that, in each of its directions ofextent, the surface region has an extent which is maximally double,still better maximally 1.5 times the extent of each of the strainsensors which is parallel to this direction of extent.

That is to say that, in regard to the extents thereof in the directionsof extent lying within the neutral reference surface, the surface regionis bounded in order to achieve the effect that the strain sensors arearranged relative to each other in substantially mirror-like manner atthe neutral reference surface and are not offset by any significantamount in one direction of extent of the neutral reference surface sothat it is thereby ensured that the elongations or compressivedistortions of the self-same volume region are captured on oppositesides of the neutral reference surface.

Furthermore, provision is preferably made for the strain sensors thatare arranged on mutually opposite sides of the respective neutralreference surface to be arranged at distances from the respectiveneutral reference surface which are such that the distances of the atleast one strain sensor on one side of the surface region of the neutralreference surface lies in a range of from 0.5 times up to 1.5 times,more preferably in the range of from 0.7 times up to 1.3 times thedistance of the at least one strain sensor on the opposite side of thesurface region.

It is thereby ensured that the distances from this surface region of thestrain sensors assigned to the respective surface region do not differtoo greatly so that it can thereby be ensured that the elongations orcompressive distortions captured by the strain sensors lie in the sameorder of magnitude.

This has the advantage that the signals produced by the strain sensorscan thereby be assigned to the respective bending load in a simplifiedmanner due to their different prefix sign.

A particularly simple arrangement of the strain sensors envisages thatthey be aligned approximately parallel to the surface region of theneutral reference surface.

Hereby, an approximately parallel alignment is to be understood asmeaning that the alignment of the strain sensors deviates by maximally±20°, more preferably by maximally ±10° from exactly parallel alignmentwith the surface region of the neutral reference surface.

For example, there is provided in this context for the strain sensors tobe arranged on sensor carrier surfaces running approximately parallel tothe surface region and to be connected thereto.

Within the framework of the embodiments of the device in accordance withthe invention described so far, no particular details of the selectedbending load have been specified.

It is particularly expedient, if the selected bending load is caused bya force on the element in the vertical direction and if the neutralreference surface arising thereby is a vertical neutral referencesurface.

A force on the element in the vertical direction is to be understood asbeing a force which is effective on the element when the device inaccordance with the invention is mounted on a motor vehicle body and themotor vehicle is standing on a horizontal carriageway.

A force in the vertical direction of this type is usually called ahitching-load which is preferably determined using a static measurementin the case of a device in accordance with the invention, i.e. when thevehicle is not being driven.

In the case of the device in accordance with the invention, ahitching-load of this type causes, in particular exclusively, a bendingload of the supporting arm due to the distance of the element forpulling a trailer and/or retaining a load carrying unit from the firstend region of the supporting arm which is connected to the motor vehiclebody, whereby, due to the solution in accordance with the invention,this load can be captured in a simple manner in the form of a staticmeasurement, i.e. when the vehicle is not being driven, and inparticular can be differentiated in a simple way from a tensile loadwhilst the vehicle is being driven along.

However, in order to also be in a position to capture tensile loads thatare effective on the element in the case of the device in accordancewith the invention, provision is preferably made for the strain sensorsto be arranged and aligned in such a manner that they capture ahorizontal tensile load by a horizontal longitudinal force on theelement.

A horizontal longitudinal force on the element is to be understood hereas being a force which acts on the element horizontally and in thelongitudinal direction of the vehicle in the case of a device inaccordance with the invention that is mounted on a vehicle body and withthe motor vehicle standing on a horizontal carriageway.

A horizontal longitudinal force of this type is usually called a tensileforce which is likewise of relevance in the case of a device inaccordance with the invention.

In particular, the determination of a tensile force of this type servesfor the determination of a trailer mass, if, in the case of a vehicle,apart from the tensile force, the acceleration in the horizontallongitudinal direction as captured by an acceleration sensor for exampleis also known.

To this end in particular, dynamic measurements of the forces acting onthe trailer or the load carrying unit are effected.

It is particularly expedient for the measurement of the horizontaltensile load, if the section of the supporting arm is selected in such amanner that the neutral reference surface of this section of thesupporting arm comprises a component in a horizontal longitudinaldirection, in particular a longitudinal direction of the vehicle, and inparticular, a significant component in the horizontal longitudinaldirection.

Preferably thereby, there is provided for the neutral reference surfaceof this supporting section to run substantially parallel to thehorizontal longitudinal direction.

A substantially parallel path of the neutral reference surface relativeto the horizontal longitudinal direction is to be understood here asmeaning that the path deviates from an exactly parallel path by an angleof less than ±30°, preferably an angle of less than ±20°.

As an alternative or in addition to the features described above, thereis provided in accordance with the invention in the case of a device ofthe type described hereinabove for the solution of the object specifiedhereinabove to be achieved in that a sensor unit comprises a sensorcarrier which is provided on mutually opposite sides with sensor carriersurfaces upon which strain sensors are arranged and connected thereto,and in that the sensor carrier is connected to a deformable supportingsection of the supporting arm in such a manner that the sensor carrierdisplays a reversible deformation behaviour which is qualitativelyidentical to the reversible deformation behaviour of the section of thesupporting arm.

This solution has the advantage that the possibility was thereby createdof not arranging the strain sensors directly on the supporting arm butrather, on a sensor carrier which is connected to a supporting armsection of the supporting arm in such a manner that it qualitativelydisplays the same elongation behaviour as the section of the supportingarm.

This thereby offers the possibility on the one hand of capturing thereversible deformation behaviour of the section of the supporting armbut, for the purposes thereof on the other hand, a sensor carrier can beemployed which can be formed independently of the supporting arm, whilethe supporting arm is to be formed in such a way that it withstands theloads arising in use of the device in accordance with the invention.

In particular thereby, the sensor carrier is arranged relative to thesection of the supporting arm in such a manner that, for capturing aselected bending load, a neutral reference surface of the supportingregion assigned to this bending load passes through a volume region ofthe sensor carrier lying between the sensor carrier surfaces.

In the case of this arrangement of the sensor carrier, it is thusensured that the strain sensors located on the sensor carrier surfacesare able to capture the pure bending loads in that the strain sensor onone side of the neutral reference surface experiences an elongation andthe strain sensor on the other side of the neutral reference surfaceexperiences a compressive distortion.

Particularly favorable, is an arrangement of the sensor carrier relativeto the section of the supporting arm in which the neutral referencesurface intersects a central volume region of the sensor carrier so thatthe spacing of the at least one strain sensor on the one side to theneutral reference surface thereby corresponds approximately to thespacing of the strain sensor on the other neutral reference surface.

The elongations can be captured in a particularly expedient manner ifthe sensor carrier extends substantially along the neutral referencesurface.

An extension substantially along the neutral reference surface is to beunderstood as meaning that the extension can deviate from an exactlyparallel path by maximally ±30°.

In particular, the sensor carrier is formed in such a way that itextends in the direction of a longitudinal central axis in bar-shaped orplate-like manner for example and in this case in particular, there isprovided for the sensor carrier surfaces to be arranged on mutuallyopposite sides of a longitudinal central axis of the sensor carrier.

In particular, provision is likewise made in the case of this solutionfor the mutually opposite sensor carrier surfaces to each be atdistances from the neutral reference surface which differ from eachother by a factor in the range of 0.5 to 1.5 in order to thus ensurethat the distances from the neutral reference surface of the strainsensors arranged on mutually opposite of the neutral reference surfaceare of the same order of magnitude, are approximately equally large.

As has already been explained above, the sensor carrier should not haveany significant effect on the reversible deformation behaviour of thesupporting region whose reversible deformation behaviour shouldqualitatively reproduce that of the sensor carriers.

For this reason, provision is preferably made for the sensor carrier tohave an effect on the reversible deformation behaviour of the supportingarm region to which it is connected that is so small that the magnitudesof the reversible deformations of the supporting arm region arising whenthe sensor carrier is present amount to at least 0.90 times, preferablyat least 0.95 times the magnitude of the reversible deformation of thesupporting arm region without the sensor carrier.

That is to say, the sensor carrier makes an insignificant contributionto the stiffness of the section of the supporting arm to which it isconnected and thus the possibility also exists of forming the sensorcarrier independently of the formation of the section of the supportingarm with the requisite stiffness.

In the simplest case, the sensor carrier can be formed such that it isconnected to the section of the supporting arm in one-piece mannerwhereby, in this case, the sensor carrier should not make any or makeonly an insignificant contribution to the stiffness of the section ofthe supporting arm so that a large degree of freedom is thereby providedin regard to the formation of the sensor carrier and the arrangement ofthe strain sensors on the sensor carrier.

As an alternative to a one-piece formation of the sensor carrier on thesection of the supporting arm, a further advantageous solution envisagesthat the sensor carrier be a component that is mountable on a section ofthe supporting arm in releasable manner.

In this case, the sensor carrier can be formed independently of thesection of the supporting arm and can also be replaced in the event ofdamage.

Furthermore, this solution has the great advantage that the sensorcarrier can thereby be manufactured with the strain sensors as a singleunit and can be employed for different supporting arms.

In principle, this solution creates the possibility of making the sensorcarrier of a material that differs from the material of the section ofthe supporting arm.

However, in order to produce as similar a thermal expansion behaviour aspossible, there is provided for the sensor carrier to consist of amaterial having the same coefficient of thermal expansion as the sectionof the supporting arm and in particular to be of the same material asthe supporting section so that a change of temperature cannot causethermal stresses in the sensor carrier due to a different thermalexpansion.

Furthermore, provision is preferably made for the sensor carrier to havemutually spaced end regions and for the sensor carrier surfaces for thestrain sensors to be located between the end regions so that the sensorcarrier extends beyond the sensor carrier surfaces by at least the endregions.

In principle, it is conceivable to connect the sensor carrier to thesection of the supporting arm over its entire extent in the directionparallel to the neutral reference surface.

It has however proved to be advantageous if only the end regions of thesensor carrier are held in the seatings arranged in the section of thesupporting arm which transmit the reversible deformations occurring inthe section of the supporting arm due to the loads thereon to the sensorcarrier so that, in particular, the section of the sensor carriercomprising the sensor carrier surfaces is only coupled to the section ofthe supporting arm by the end regions.

In order to enable the reversible deformations of the section of thesupporting arm to be transmitted to the sensor carrier in a simple way,provision is preferably made for the end regions to engage in theseseatings in the section of the supporting arm which fix the end regionsin positive-locking manner and which transmit to the sensor carrier thereversible deformations of the section of the supporting arm thatcomprises the seatings and in addition extends between the seatings.

That is to say that in this case, due to the positive-locking connectionbetween the seatings and the section of the supporting arm and the endregions of the sensor carrier, a simple qualitative transmission of thereversible deformations of the section of the supporting arm to thesensor carrier is possible.

In particular, it is favorable if the seatings comprise seating surfaceswhich have at least one component that extends parallel to therespective neutral reference surface and acts on the end regions.

In regard to the transmission of the reversible deformation behaviour ofthe section of the supporting arm to the sensor carrier, it isparticularly expedient if the end regions comprise positive-lockingsurfaces having at least one component extending parallel to therespective neutral reference surface so that, in particular, anadvantageous transmission of the reversible deformation behaviour fromthe section of the supporting arm to the sensor carrier is effected viathis positive-locking arrangement.

Within the framework of the previous explanation of the individualexemplary embodiments, no particular details of how the sensor carriershould run relative to the section of the supporting arm have beengiven.

The basic requirement is however, that the sensor carrier for therespective bending load that is to be captured should exhibit the sameelongation behaviour as the section of the supporting arm.

In particular, apart from the bending loads, in order to also enablehorizontal tensile loads in the longitudinal direction and in particularin the longitudinal direction of the vehicle to be captured, provisionis preferably made for the sensor carrier and in particular thelongitudinal central axis thereof to have at least one component whichextends in a horizontal longitudinal direction.

The horizontal longitudinal direction is likewise to be understood—asalready mentioned above—as being a horizontal longitudinal direction inthe case of a motor vehicle having the device in accordance with theinvention mounted thereon standing on a horizontal carriageway.

It is particularly expedient if the sensor carrier extends substantiallyparallel to the horizontal longitudinal direction, whereby asubstantially parallel extension relative to a horizontal longitudinaldirection is to be understood as being a deviation of ±30°, preferablyof ±20° from an exactly parallel path relative to the horizontallongitudinal direction.

In particular, the horizontal longitudinal direction is a horizontaldirection running parallel to the longitudinal direction of the vehicle.

Up to now, no particular details in regard to the arrangement of thesensor carrier relative to the section of the supporting arm itself havebeen given.

Thus, one advantageous solution envisages that the sensor carrier bearranged beside the section of the supporting arm and offset in adirection parallel to the respective neutral reference plane.

For example, this is effected in that the sensor carrier is arranged ata long side of the section of the supporting arm.

Another advantageous solution envisages that the section of thesupporting arm comprise a recess and that the sensor carrier be arrangedsuch as to engage in the recess in the section of the supporting arm.

It is not necessary for the sensor carrier to engage entirely in therecess in the section of the supporting arm, in particular, it sufficesfor the advantageous formation of the seatings for the end regions ofthe sensor carrier, if the sensor carrier only partly engages in therecess in the section of the supporting arm.

Up to now, no particular details in regard to the location of thesection of the supporting arm have been given.

Thus, one advantageous solution envisages that the section of thesupporting arm as measured along the selected neutral reference surfacebe at a distance from the first end region which lies in the range offrom 0.3 times up to 2 times the distance from the second end region.

A particularly expeditious solution envisages that a curved piece beprovided between an intermediate region of the supporting arm comprisingthe section of the supporting arm and the first end region and/or thesecond end region of the supporting arm.

Moreover, one expeditious solution envisages that the section of thesupporting arm lies in a central region between the first end region andthe second end region of the supporting arm.

Up to now, no particular details in connection with the strain sensorsthat are employed have been given.

In principle, any kind of strain sensor is usable.

A particularly expedient solution however envisages that the strainsensors comprise strain gauges.

In order to exclude temperature effects, provision is preferably madefor the strain sensors to be temperature-compensated.

One possible realization of a temperature-compensated strain sensorenvisages that it comprise a plurality of strain gauges, four forexample, which are interconnected in a bridge circuit, for example, in aWheatstone bridge circuit.

Likewise up to now, no particular details in regard to the evaluation ofthe sensor signals have been given.

Thus within the scope of the solution in accordance with the invention,it would be conceivable for an evaluating unit to be provided in themotor vehicle.

One particularly expedient solution however envisages that an evaluatingunit which evaluates the signals of the strain sensors be provided onthe device itself.

This has the advantage that the signals of the strain sensors do notthen have to be passed on over large distances and thus be subjected tofurther interference effects.

Preferably hereby, provision is made for the evaluating unit to bearranged on the carrier unit or on the supporting arm.

In the case where use is made of a sensor carrier, the evaluating unitis preferably provided on the sensor carrier so that the strain sensorsprovided directly on the sensor carrier can be connected to theevaluating unit and thus the sensor unit itself also comprises theevaluating unit so that the sensor unit is employable and in particularmountable as an independent unit on the respective supporting arm.

In this manner, the evaluating unit can work in the most varied ofmanners.

One solution envisages that the evaluating unit determines the forceacting on the element in the vertical direction.

A further advantageous solution envisages that the evaluating unitdetermines a horizontal transverse force.

A further advantageous solution envisages that the evaluating unitdetermines a horizontal longitudinal force.

Furthermore in particular, it is of advantage for the solution inaccordance with the invention if an acceleration sensor is assigned tothe evaluating unit.

The acceleration sensor can be arranged on either the carrier unit orthe supporting arm independently of the evaluating unit.

A particularly expedient solution however envisages that theacceleration sensor be provided in the evaluating unit.

In principle, the acceleration sensor can capture a multiplicity ofaccelerations.

For example, the accelerations can be in the vertical direction and inthe horizontal transverse direction.

A particularly expedient solution envisages that the acceleration sensorcapture at least one acceleration in the horizontal longitudinaldirection since in this case it is then possible to determine the massof the trailer attached to the element or of the load carrying unitattached to the element by taking into consideration the horizontallongitudinal force, i.e. in particular the tensile force and theacceleration in the horizontal longitudinal direction.

A particularly advantageous solution envisages that the supporting armbe a ball neck which carries a coupling ball at its second end as anelement for attaching a trailer and/or fixing a load carrying unit.

Further features and advantages of the invention form the subject matterof the following description as well as the drawings of some exemplaryembodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a side view of a motor vehicle with a first exemplaryembodiment of a device in accordance with the invention;

FIG. 2 a schematic illustration of the first exemplary embodiment of thedevice in accordance with the invention depicting bending and tensileloads;

FIG. 3 a view of the first exemplary embodiment in the direction of thearrow A in FIG. 2;

FIG. 4 a section along the line 4-4 in FIG. 2;

FIG. 5 an illustration of the first exemplary embodiment with strainsensors;

FIG. 6 a section along the line 6-6 in FIG. 5;

FIG. 7 an enlarged illustration of the arrangement of the strain sensorsrelative to a respective surface region of the respective neutralreference surface;

FIG. 8 an illustration similar to FIG. 2 of a second exemplaryembodiment of the device in accordance with the invention;

FIG. 9 an enlarged view of the second exemplary embodiment in thedirection of the arrow B in FIG. 8;

FIG. 10 a section along the line 10-10 in FIG. 8;

FIG. 11 a rear view of a vehicle with a third exemplary embodiment of adevice in accordance with the invention;

FIG. 12 an enlarged view of the device in accordance with the inventionin a working position with removed bumper unit;

FIG. 13 an enlarged view similar to FIG. 12 of the device in accordancewith the invention in a resting position with removed bumper unit;

FIG. 14 an illustration of the supporting arm in accordance with thethird exemplary embodiment depicting the effective forces and thematerial bending stresses and material tensile stresses resultingtherefrom;

FIG. 15 a view of the supporting arm in accordance with FIG. 14 inaccord with the arrow C in FIG. 14;

FIG. 16 an illustration of the supporting arm in accord with FIG. 14depicting the provided strain sensors;

FIG. 17 an illustration of a supporting arm in accordance with a fourthexemplary embodiment of the device in accordance with the invention;

FIG. 18 an enlarged side elevational view of the supporting arm inaccordance with FIG. 17;

FIG. 19 a perspective illustration of a supporting arm in accordancewith a fifth exemplary embodiment;

FIG. 20 an illustration of the supporting arm in accordance with FIG. 19in the direction of the arrow D in FIG. 19;

FIG. 21 an illustration of the supporting arm in accordance with FIG. 19in the direction of the arrow E in FIG. 19;

FIG. 22 an illustration of the supporting arm in accordance with a sixthexemplary embodiment of the device in accordance with the invention;

FIG. 23 an enlarged illustration of the supporting arm section of thesupporting arm in accordance with FIG. 22;

FIG. 24 a lateral plan view of the supporting arm section of thesupporting arm in accordance with FIG. 22 and

FIG. 25 a section along the line 25-25 in FIG. 23.

DETAILED DESCRIPTION OF THE INVENTION

A motor vehicle that is referenced 10 as a whole comprises a motorvehicle body 12 which is provided with a carrier unit 20 in a tailregion 14 namely, close to a floor 16 of the vehicle wherein the carrierunit comprises a cross beam 22 for example which is connected to thetail region 14 close to the floor 16 of the vehicle.

The connection between the cross beam 22 can, for example, be effectedby mounting flanges located in the tail region 14 or for example, bymeans of side members 26 which extend in a longitudinal direction 24 ofthe vehicle and, as is known, are likewise located on sections 28 of thevehicle body that extend in the longitudinal direction 24 of thevehicle.

A supporting arm that is referenced 30 as a whole is connected to thecarrier unit 20 in that a first end 32 of the supporting arm is heldeither directly or by a bearing unit on the carrier unit 20.

In the first exemplary embodiment of the supporting arm 30 that isillustrated in FIG. 1, there is a direct connection of the first end 32of the supporting arm 30 to the cross beam 22.

The supporting arm 30 carries at a second end 34 thereof locatedopposite the first end 32 an element 40 which is provided for attachinga trailer or for fixing a load carrying unit for example.

For example, seen here is an element 40 of this type in the form of acoupling ball which, as is usually the case, permits connection to aball joint coupling of a trailer.

However, the coupling ball also permits the simple mounting of a loadcarrying unit since commonly used load carrying units are likewisefrequently constructed such that they are mountable on a coupling ball40 and, in addition, they are also supportable on the supporting arm 30if necessary.

The element 40 sits for example on a carrier 42 which is connected tothe second end region 34 of the supporting arm 30 and extends away froma side of the carrier 42 remote from a carriageway 44 in the directionof a central axis 46 which runs approximately vertically when thecarriageway 44 is horizontal and also runs through a central point 48 ofthe ball in the case of the coupling ball.

For improving the aesthetic effect, the cross beam 22 is preferablyarranged under a rear-end bumper unit 50 of the motor vehicle body 12whereby for example, the bumper unit 50 covers the cross beam 22 and thefirst end 32 of the supporting arm 30.

In the first exemplary embodiment, the supporting arm 30 is illustratedschematically as being a rectangular bar although the supporting arm 30can be of any arbitrary shape as will be evident from the followingexemplary embodiments.

The illustration of the supporting arm 30 in the form of a rectangularbar in connection with the first exemplary embodiment makes it possibleto also illustrate in a simplified manner the relationships that areessential for the invention when the element 40 is loaded by forcesacting in different directions and the reversible deformations resultingtherefrom.

In the case of the element 40 being loaded by a vertical force FZ whichis effective on the element 40 in the vertical direction and correspondsto the hitching-load of a trailer or a load carrying unit that is actingon this element 40 then, for example, a bending load of the supportingarm 30 occurs when the force FZ acts on the element 40 from above in thedirection of the force of gravity as a result of which there occurs areversible bending of the supporting arm 30 in the direction of thecarriageway 44. This builds up, in particular, in a section 60 of thesupporting arm that is located between the first end 32 and the secondend 34 which is unaffected by the connection between the first end 32 ofthe supporting arm 30 and the cross beam 22 and is also unaffected bythe connection of the second end 34 of the supporting arm 30 to theelement 40, for example, to a carrier 42 for the element 40.

The force FZ effective in the vertical direction and in the direction ofthe force of gravity thus produces a vertical bending load at least inthe section 60 of the supporting arm. This leads to the section 60 ofthe supporting arm being stretched on an upper transverse side 62thereof taken with respect to the gravitational force and experiencingcompressive distortion on a lower transverse side 64 taken with respectto the direction of the force of gravity so that material bendingstresses MBS_(Z) caused by the bending moment occur close to the uppertransverse side 62, whilst material bending stresses −MBS_(Z) which aredue to the material compressive distortions at the lower transverse side64 occur close to the lower transverse side 64 of the section of thesupporting arm.

Consequently, due to the material distortions MBS_(Z) and −MBS_(Z) beingof opposite sign, a so-called neutral axis that is referred tohereinafter as the vertical neutral axis NFV in which no materialstresses and thus no elongation and no compressive distortion of thematerial arises is formed therebetween in the presence of a verticalbending loading BV.

Usually, as illustrated in FIG. 4, the vertical neutral axis NFV islocated in the centroid FS of any cross-sectional area QF of the section60 of the supporting arm and thus, for example, to a first approximationcentrally between the upper transverse side 62 and the lower transverseside 64.

In the case where the force FZ is directed exclusively in the verticaldirection, the section 60 of the supporting arm comprises a verticalneutral layer NSV which extends over the entire width of the section 60of the supporting arm and is determined by a vertical neutral referencesurface NRFV which runs on the one hand through the vertical neutralaxis NFV and, in a direction transverse to the vertical neutral axisNFV, runs in particular perpendicularly to the vertical neutral axis NFVand in particular too, perpendicularly to a bending movement surfaceBBFV that is formed in the presence of the vertical bending load BV.

The vertical bending movement surface BBFV is defined as the surfacewhich runs through the neutral axis NFV and parallel to which thesection 60 of the supporting arm moves the least possible and inparticular without any transverse movements in the presence of thevertical bending loading BV.

In particular, the vertical neutral reference surface NRFV runs, to anapproximation, perpendicularly to a central surface MF of the section 60of the supporting arm which is parallel to the vertical and runs througha respective centroid FS of each cross-sectional area QF of the section60 of the supporting arm and thus through the vertical neutral axis NFV.

If, by contrast, a load is imposed on the element 40 by a horizontaltransverse force FY that is aligned perpendicularly to the verticalforce FZ and, for example, also runs perpendicularly to the centralsurface MF, then bending of the supporting arm 60 occurs which is suchthat a material elongation and thus a positive material bending stressMBS_(Y) occurs on a long side 66 which extends between the uppertransverse side 62 and the lower transverse side 64, whereas on theoppositely located long side 68 which likewise extends between the uppertransverse side 62 and the lower transverse side 66 there is a materialcompressive distortion and thus a negative material bending stress−MBS_(Y).

A transverse bending loading BQ of this type likewise leads to theformation of a transverse neutral axis NFQ which coincides with theneutral axis NFV in the case of the exemplary embodiment illustrated inaccord with FIG. 4 due to the symmetrical construction of the section 60of the supporting arm.

This, however, is not necessarily the case. In the event of the section60 of the supporting arm having an asymmetrical construction, theneutral axis NFQ can run in a different manner and be located elsewherethan the neutral axis NFV.

When loaded by the horizontal transverse force FY, a transverse neutrallayer NSQ is likewise formed in the section 60 of the supporting arm inwhich there is no elongation or compressive distortion of the materialand thus too no material stresses MS occur.

Hereby, the neutral layer NSQ extends in a transverse neutral referencesurface NRFQ running perpendicularly to the horizontal transverse forceFY which, for example, coincides with the central surface MF in the caseof this simplified exemplary embodiment.

However, in the case where the transverse neutral reference surface NRFQdoes not coincide with the central surface MF, the transverse neutralreference surface NRFQ runs on the one hand through the transverseneutral axis NFQ and moreover, perpendicularly to a transverse bendingmovement surface BBF which runs through the neutral axis NFQ andparallel to which the section 60 of the supporting arm moves with thelowest possible and in particular without any transverse movements inthe presence of the transverse bending loading BQ.

In addition, for example, the transverse neutral reference surface NRFQalso runs perpendicularly to the vertical neutral reference surfaceNRFV, this being due to the fact that the vertical force FZ and thehorizontal transverse force FY run perpendicularly to each other.

In addition, a tensile loading of the element 40 can be produced by ahorizontal longitudinal force FX which correspond to an accelerationforce that runs perpendicularly to the vertical force FZ andperpendicularly to the horizontal transverse force FY and for example,is directed away from the tail region 14 of the motor vehicle body 12 sothat, due to the horizontal longitudinal force FX, tensile stressesMZS_(X) are formed in the section 60 of the supporting arm which howeverrun parallel to each other and in the same direction over the respectivecross-sectional areas QF and, to a first approximation, are equallylarge, whereby the horizontal longitudinal force FX is preferablyaligned approximately parallel to the longitudinal direction 24 of thevehicle when the motor vehicle 10 is travelling on a horizontalcarriageway.

In the simplified first exemplary embodiment, the supporting arm 30 isaligned in such a way that it runs horizontally and in parallel with thelongitudinal direction 24 of the vehicle so that the horizontallongitudinal force FX leads exclusively to uniform material elongationover the respective cross-sectional area QF and thus to equally largematerial stresses MZS_(X).

Hereby, the load carrying unit 20, the supporting arm 30 and the element40 form a device 70 in accordance with the invention for pulling atrailer and/or retaining a load carrying unit.

For collecting the reversible deformation data of the section 60 of thesupporting arm resulting from the differing loads imposed by thevertical force FZ, the horizontal transverse force FY and the horizontallongitudinal force FX in the first exemplary embodiment, the supportingarm 30 is provided in the section 60 of the supporting arm with strainsensors 72 and 74 which are arranged on the transverse sides 62 and 66[sic] and strain sensors 76 and 78 which are arranged on the long sides66 and 68.

The strain sensors 72 and 74 are arranged on both sides of a surfaceregion FB_(NRFV) which represents a partial surface of the verticalneutral reference surface NRFV and exhibits in the different directionsof extent ARX, ARY thereof lying in the vertical neutral referencesurface NRFV a maximal extent of 1.5 times that exhibited by the strainsensors 72, 74 in these directions of extent (FIGS. 6, 7).

Furthermore, a vertical projection of the strain sensors 72, 74 onto thevertical neutral reference surface NRFV lies within the surface regionFB_(NRFV) as is illustrated in FIGS. 5 and 7 on the basis of the strainsensor 72.

Thus, the strain sensors 72 and 74 capture the material stresses MBSwithin the same volume region of the section 60 of the supporting armthat are produced by the vertical bending load and detect opposedmaterial bending stresses in the presence of the vertical bending loadwhich lead to signals of reverse prefix sign although in the same orderof magnitude and preferably of approximately the same size in the caseof the strain sensors 72, 74 that are arranged in the first exemplaryembodiment at substantially the same distance from the vertical neutralreference surface NRFV.

Thus, for example, in the case of a static load produced by the forceFZ, this can be determined by the strain sensors 72, 74, whereby, in thecase of the device in accordance with the invention, the force FZrepresents a hitching-load of a trailer or a load carrying unit which isacting on the element 40 of the supporting arm 30.

In a comparable way, the strain sensors 76 and 78 are also arranged onmutually opposite sides of the transverse neutral reference plane NRFQand are arranged relative to a surface region FB_(NRFQ) in such a waythat the strain sensors 76 and 78 lie within the surface regionFB_(NRFQ) in the case of a vertical projection onto the transverseneutral reference surface NRFQ, whereby the surface region FB_(NRFQ)exhibits in the directions of extent thereof lying in the surface regionFB_(NRFQ) a respective extent which maximally corresponds to 1.5 timesthe extent of the strain sensors 76, 78 parallel to these directions.

Moreover, a vertical projection of the strain sensors 76 and 78 alsolies within the surface region FB_(NRFQ).

Due to the arrangement of the strain sensors 76, 78 at approximately thesame distance from the transverse neutral reference surface NRFQ, atransverse bending load BQ likewise results in signals of reversedprefix sign although they are in the same order of magnitude and arepreferably of approximately the same size in the case of the strainsensors 76, 78.

The horizontal transverse force FY determined by the sensors 76, 78represents, in particular in the case of the device in accordance withthe invention, a lateral acceleration on the element 40 which arises forexample whilst the motor vehicle is being driven in the event of rollingmotions of the motor vehicle or of the motor vehicle with the trailer orwith the load carrying unit.

Under the effect of the horizontal longitudinal force FX, the sameelongations arise everywhere in the section 60 of the supporting arm sothat in essence, all the strain sensors 72, 74, 76, 78 capture the samematerial bending stresses MZS.

In particular in the case of the device in accordance with theinvention, a horizontal longitudinal force FX of this type represents atensile force when the motor vehicle is being driven along which acts onthe element 40. With knowledge of the acceleration, the mass of thetrailer acting on the element 40 or of the load carrying unit acting onthe element 40 can be determined from this tensile force.

In the solution in accordance with the invention, there is provided inparticular an evaluating unit AU which collects the signals of thestrain sensors 72, 74 and also possibly 76, 78 as well and from these itdetermines the hitching-load FZ on the element 40 in the stopped stateof the motor vehicle, for example, by consulting a table whichassociates the signals of the strain sensors with a hitching-load, andthereafter, whilst being driven and by taking into consideration themeasured hitching-load FZ, it determines the tensile force FX and ifnecessary the transverse force FY, likewise for example, by consulting atable which links the values for the hitching-load and the signals ofthe strain sensors when it is being driven with a value for the tensileforce.

If, in addition, an acceleration sensor BSH for determining theacceleration in the horizontal longitudinal direction X is provided inthe evaluating unit AU, then the evaluating unit AU is also able todetermine the mass of a trailer engaging the element 40 or the mass of aload carrying unit held on the element 40. By virtue of the arrangementof the acceleration sensor BSH together with the evaluating unit, thevalue for the acceleration is readily available time-synchronously withthe tensile force FX for determining the mass.

For capturing the reversible deformations of the section 60 of thesupporting arm under the most diverse of loads by the vertical force FZ,the horizontal transverse force FY and the horizontal longitudinal forceFX, the section 60 of the supporting arm is provided with abreak-through 80 in the case of a second exemplary embodiment that isillustrated in FIGS. 8 to 10 which, for example, extends from the longside 66 to the long side 68 and approximately parallel to the verticalneutral reference surface NRFV and lies on both sides of the neutralreference plane NRFV, whereby the stability of the section 60 of thesupporting arm on both sides of the break-through 80 is ensured by anupper flange 82 and a lower flange 84 of the section 60 of thesupporting arm.

The break-through 80 only impairs the stability of the supporting arm 30and thus too of the section 60 of the supporting arm in regard to adeflection under a bending load imposed by the vertical force FZ to aninsignificant amount. This is because, in the event of such a load, asexplained above, only very slight material stresses MBS_(Z) occur closeto the neutral reference plane NRFV which runs on the one hand throughthe neutral axis NFV and on the other hand transverse thereto and inparticular perpendicularly relative to the bending loading surface BBFV,and these stresses do not make any substantial contribution to thestability of the supporting arm 30 against a vertical bending loadingresulting from the application of the vertical force FZ.

A sensor unit, which is designated as a whole by 90, is arranged in thisbreak-through 80 and comprises a sensor carrier 92 that extends in alongitudinal direction 93 and is arranged in such a way that the neutralreference plane NRFV cuts through the sensor carrier 92 in a centralvolume region 94.

Furthermore, the sensor carrier 92 comprises sensor carrier surfaces102, 104 which are located on mutually opposite sides of the verticalneutral reference surface NRFV and are preferably at substantially thesame distance from the vertical neutral reference surface NRFV and runsubstantially parallel to the vertical neutral reference surface NRFV.Strain sensors 106 and 108 which capture material elongations arearranged on these sensor carrier surfaces 102 and 104.

The sensor carrier 92 is connected fixedly to the section 60 of thesupporting arm by a first end region 112 and a second end region 114between which the sensor carrier surfaces 102 and 104 respectively liebut extends at least within the region of its sensor carrier surfaces102 and 104 independently of the section 60 of the supporting arm sothat the strain sensors 106 and 108 resting on the sensor carriersurfaces 102 and 104 capture exclusively the elongations occurring inthe sensor carrier 92 on both sides of the vertical neutral referencesurface NRFV.

The connection of the first end region 112 and the second end region 114of the sensor carrier 92 to the section 60 of the supporting arm iseffected in such a way that the sensor carrier 92 experiencesqualitatively the same material stresses MBS_(Z) as would acorresponding volume region of the section 60 of the supporting armexperience them.

For example, the connection between the first end region 112 and thesecond end region 114 of the sensor carrier 92 is effected through therecesses 116 and 118 which are provided in the section 60 of thesupporting arm on both sides of the break-through 80 and which receivethe end regions 112 and 114 in a form-fitting manner and thus at leastqualitatively transmit the reversible deformations arising in thesection 60 of the supporting arm to the sensor carrier 92.

In the solution in accordance with the invention, the strain sensors 106and 108 are preferably arranged on mutually oppositely located sides ofthe vertical neutral reference surface NRFV, namely on both sides of asurface region FB_(NRFV) which, in the respective directions of extent,exhibits maximally an extent of 1.5 times that of the strain sensors 106and 108 so that the strain sensors 106, 108 are arranged insubstantially mirror-like manner relative to the vertical neutralreference surface NRFV in order to capture the elongations orcompressive distortions that arise.

Furthermore, the distances A102 and A104 of the sensor carrier surfaces102 and 104 from the vertical neutral reference surface NRFV arepreferably selected in such a way that one of the distances A102, A104amounts to maximally 1.5 times that of the other one of the distancesA104 or A102.

Thus, elongations of the sensor carrier 92 which arise on both sides ofthe same surface region FB_(NRFV) of the vertical neutral referencesurface NRFV and which—as described above—in the case of a deflection ofthe section 60 of the supporting arm, exhibit different prefix signs andlie in the same order of magnitude can be captured and, in the case of apurely tensile loading of the sensor carrier 92, simultaneouslyoccurring elongations can be captured by both strain sensors 106, 108 asexplained above.

If, additionally, the bending movements which the horizontal transverseforce FY produces as was described in FIG. 2 should also need to becaptured then the sensor carrier 92 is provided with sensor carriersurfaces 122, 124 which run transverse to the sensor carrier surfaces102 and 104 and are arranged on mutually oppositely located sides of thetransverse neutral reference surface NRFQ and upon which the strainsensors 126 and 128 are arranged.

The sensor carrier 92 is coupled to the section of the supporting arm 16by the fixture of its end regions 112 and 114 in the recesses 116 and118 in such a manner that even when the supporting arm 30 is subjectedto loads by the horizontal transverse force FY, the sensor carrier 92qualitatively displays the same bending movements as the section 60 ofthe supporting arm in the region of the upper flange 82 and the lowerflange 84.

The strain sensors 126, 128 serve for capturing the elongationscorresponding to the material stresses MBS_(Y) and −MBS_(Y).

The sensor carrier surfaces 122, 124 are also arranged at distances A122and A124 from the transverse neutral reference surface NRFQ, whereby oneof the distances A122, A124 is less than 1.5 times that of the distanceA124 or A122.

Furthermore, the strain sensors 126 and 128 are located on oppositesides of a surface region FB_(NRFQ), whereby the surface regionFB_(NRFQ) has an extent in the individual directions of extent which ismaximally 1.5 times that of the corresponding extent of the respectivestrain sensor 126, 128 so that the strain sensors 126, 128 are arrangedon both sides of the neutral reference surface NRFQ in substantiallymirror like manner with respect thereto and thus capture the elongationof the material of the sensor carrier 92 at substantially the same placeon opposite sides of the neutral reference surface NRFQ.

In a similar manner, the strain sensors 126 and 128 react in the sameway to elongations due to the horizontal longitudinal force FX in such amanner that they capture the same elongation on both sides of the sensorcarrier 92, as is also the case with the strain sensors 106 and 108.

In particular, the positioning of the seatings 116 and 118 relative tothe first end region 32 of the supporting arm 30 and the second endregion 34 of the supporting arm 30 is effected in such a manner that thespacings AE116 and AE118 thereof relative to each other are measuredsuch that one of the distances AE116, AE118 amounts to less than 1.5times the other one of the spacings AE118 or AE116, and in particular,the two spacings AE116 and AE118 are substantially equally large.

Thus, the sensor carrier 92 with the respective strain sensors 106 and108 or 126 and 128 permits the effects of the vertical bending loadingBV, the transverse bending loading BQ and the horizontal tensile load bythe force in the longitudinal direction FX to be captured eitherseparately or else by superimposition thereof.

In particular hereby, it is essential that, in the presence of thebending loads, the strain sensors 106, 108 or 126, 128 capture thematerial bending stresses of differing prefix signs, i.e. elongations onthe one hand and compressive distortions on the other, on opposite sidesof the corresponding vertical neutral reference surface NRFV and NRFQ,whilst the strain sensors 106 and 108 or 126 and 128 capture the samematerial stresses on both sides of the respective vertical neutralreference surface NRFV or the transverse neutral reference surfaces NRFQwhen the horizontal longitudinal force FX is effective substantially inthe respective cross-sectional areas QF of the section 60 of thesupporting arm.

Thus, the vertical bending load and the horizontal bending load can eachbe produced separately or else superimposed on the horizontal tensileload measuring signals of the strain sensors 106 and 108 or 126 and 128,this then permitting a conclusion to be drawn in regard to theindividual components of the vertical force FZ, the horizontaltransverse force FY and the horizontal longitudinal force FX.

Furthermore, in the second exemplary embodiment, those elements whichare identical with those of the preceding exemplary embodiments areprovided with the same reference symbol so that reference can be made tothe expositions in regard to the preceding exemplary embodiments.

In a third exemplary embodiment of a device in accordance with theinvention which is illustrated in FIGS. 10 to 13, the carrier unit 20 islikewise provided in the tail region 14 of the motor vehicle body 12 ofthe motor vehicle 10 which, for example, likewise comprises the crossbeam 22 that is connected by means of side members 26 to the tail region14 of the motor vehicle body 12.

Furthermore, the cross beam 22 is arranged such that it is covered bythe bumper unit 50.

The supporting arm 130 likewise carries the element 40 which is in theform of a coupling ball, whereby, as is illustrated in particular inFIGS. 11 and 12, the supporting arm 30 extends from a swivel joint unit140 to which the supporting arm 130 is connected at its first end region132, whereby, for example, a swivel joint body 142 of the swivel jointunit 140 is formed at the first end region 132.

The supporting arm 130 in this exemplary embodiment then extends fromthe first end region 132 over a first curved piece 144 up to anintermediate piece 146 to which there is adjoined a second curved piece148 that carries the element 40 in the form of a coupling ball, wherebyyet another ball lug 152 is provided between the element 40 in the formof a coupling ball and the second curved piece 148.

The second curved piece 148 then forms the end region 134 of thesupporting arm 130 which then for example, carries the ball lug 152 towhich the element 40 in the form of a coupling ball is adjoined.

For easy mounting of a contact unit as illustrated in FIGS. 12 and 13,an annular body 154 which surrounds a passage 156 in which a contactunit can be mounted is formed on the supporting arm 130 in the secondcurved piece 148.

Preferably, the annular body 154 is arranged in the second curved piece148 in such a manner that, following the annular body 154, a transitioninto the intermediate piece 146 of the supporting arm 130 is effected bymeans of an adapter piece 158.

The swivel joint body 142 of the swivel joint unit 140 is mounted in aswivel joint seating 162 such that it is able to swivel about aswivelling axis 160 which, in particular, is inclined to a verticalvehicle longitudinal central plane 18, which said seating holds theswivel joint body 142 such that it is rotatable about the swivellingaxis 160 on the one hand and, on the other hand, comprises a lockingunit (not illustrated) which enables non-rotatable arrest of thesupporting arm 130 with respect to swivelling movements about theswivelling axis 160.

For its part, the swivel joint body seating 162 is then in turn firmlyconnected to the cross beam 62 by means of a swivel joint base 164.

In this third exemplary embodiment as is illustrated in FIGS. 11, 12 and13, the supporting arm 130 is pivotal from a working position A that isillustrated in FIGS. 11 and 12 in which the element in the form of acoupling ball 40 is positioned in such a way that it is located behindthe bumper unit 50 on a side remote from a carriageway 42, into aresting position R that is illustrated in FIG. 13 in which the element40 is arranged such that it faces the carriageway 42.

The element 40 is thereby movable under a lower edge 52 of the bumperunit 50.

In particular, in the working position A, the supporting arm 130 extendssubstantially in the vertical vehicle longitudinal central plane 18,whereby the latter intersects the element 40 centrally in the case whereit is constructed in the form of a coupling ball so that a vertical ballcentral axis 44 lies in the longitudinal central plane 18.

In the case of the supporting arm 130 in accordance with the thirdexemplary embodiment, it is formed approximately U-shaped by virtue ofthe first curved piece 144, the intermediate piece 146 and the secondcurved piece 148 and, in the working position A in which the loads areimposed on the element 40 and these are to be captured, it is aligned insuch a way that, for example, the forces FX and FZ which are acting onthe element 40 and in particular, the central point of the ball 46 aretransmitted via the approximately U-shaped supporting arm 130 to theswivel joint body 142 of the swivel joint unit 140, whereby theswivelling axis 160 represents a centre point of the force pick-up bythe swivel joint unit 140.

In this third exemplary embodiment, the intermediate piece preferablycomprises the section 60 of the supporting arm in which the process ofcapturing the reversible deformations is to be effected. These, forexample, are effective on the supporting arm 130 due to the forces FXand FZ (FIG. 14).

It is to be noted that the vertical force FZ acting on the element 40 inthe direction of the force of gravity also leads to a pure bendingthereof in the region of the intermediate piece 146 so that there islikewise a formation of a vertical neutral axis NFV and a verticalneutral reference surface NRFV in the section 60 of the supporting arm,whereby the neutral reference surface NRFV runs through the verticalneutral axis NFV and transverse to the vertical bending movement surfaceBBFV which itself extends parallel to the vertical force FZ in thedirection of the force of gravity and defines the surface in which thesupporting arm 130 moves when being subjected to the vertical force FZin the direction of the force of gravity FZ and thereby yields as littleas possible in a direction transverse thereto.

Hereby, as is illustrated in FIGS. 12 and 13 in the case of a supportingarm 130, the bending movement surface BBFV does not run exactly parallelnor coincide with the vehicle longitudinal central plane 18 but rather,it is inclined with respect thereto at least in sections thereof sincethe supporting arm 130 likewise does not run symmetrically relative tothe vertical vehicle longitudinal central plane 18 as is illustrated inFIG. 12.

An exemplary depiction of the vertical bending movement surface BBFVwhen loaded by the vertical force FZ in the direction of the force ofgravity FZ is illustrated in FIG. 15 for example.

Thus, the loading of the supporting arm 130 by the vertical force FZ inthe direction of the force of gravity leads to a bending load in thesection 60 of the supporting arm in the same way as was the case in thefirst and second exemplary embodiment.

The arrangement of the section 60 of the supporting arm for capturingthe reversible deformations thereof is effected in the case of thesupporting arm 130 in the intermediate piece 146 since this extendsbetween the curved pieces 144 and 148 with a sizeable component thereofextending parallel to the horizontal longitudinal direction X in whichthe horizontal longitudinal force FX is acting so that elongationsrunning parallel to the horizontal longitudinal direction X arise in thesection 60 of the supporting arm.

In contrast to the first and second exemplary embodiment however, due tothe different geometrical design of the supporting arm 130, a horizontallongitudinal force FX does not lead exclusively to purely materialtensile stresses MZS_(X) in the section 60 of the supporting arm butrather additionally, to a material bending stress MBS_(X) since thehorizontal longitudinal force FX acts on the section 60 of thesupporting arm by means of a lever arm H1 and, moreover, the supportingsection 60 in turn acts via the lever arm H2 on the swivel joint body142 which ultimately fixes the supporting arm 130.

Thus, in contrast to the first and second exemplary embodiment and as isillustrated in FIG. 14, the horizontal longitudinal force FX results inthe occurrence in the section 60 of the supporting arm in the region ofthe respective cross-sectional areas QF of both material tensilestresses MZS_(X) which exhibit the same prefix sign over the entirecross section as well as material bending stresses MBS_(X) which exhibitone prefix sign on the one side of the vertical neutral referencesurface NRFV and a differing prefix sign on the opposite side.

This has the consequence that in the case of the horizontal longitudinalforce FX the material tensile stresses MZS_(X) and the material bendingstresses MBS_(X) are added to each other and are thus superimposed inthe section 60 of the supporting arm.

For capturing the different material bending stresses MBS_(Z) andMBS_(X) as well as the material tensile stresses MZS_(X) and as isillustrated in FIG. 16 for example, strain sensors 172 and 174 areprovided on both sides of the bounded surface region FB_(NRFV) of thevertical neutral reference surface NRFV, whereby said sensors restdirectly upon the outer surfaces of the intermediate piece 146 forexample and thus capture the elongations arising on both sides of thevertical neutral reference surface NRFV.

Preferably thereby, the strain sensors 172 and 174 are arranged atdistances A172 and A174 from the neutral reference surface NRFZ whichare approximately equally large, and are preferably of a size such thatthe one of the distances A172, A174 amounts to less than 1.5 times thatof the distances A174 or A172.

That is to say, that under the effect of the vertical force FZ, one ofthe strain sensors 172, 174 measures an elongation and the other one ofthe strain sensors 174 or 172 measures a compressive distortion,depending upon whether the vertical force FZ is acting in the directionof the force of gravity or in a direction opposite to the direction ofthe force of gravity.

If, on the other hand, the horizontal longitudinal force FX is acting onthe element 40 then, for example, one of the strain sensors 172, 174measures a smaller elongation than the other one of the strain sensors172, 174 since the sum of the material tensile stresses MZS_(X) and thematerial bending stresses MBS_(X) have an effect upon the elongationsthat are to be measured.

Thus, in the third exemplary embodiment, the possibility likewise existsof determining the force FZ and thus the hitching-load from the signalsof the strain sensors 172, 174 with the aid of the evaluating unit AU inthe static condition, i.e. when it is not being driven, and ofdetermining the mass of the trailer or the load carrying unit when it isbeing driven given a knowledge of the hitching-load FZ, the tensileforce FX and by taking into consideration the acceleration in thehorizontal longitudinal direction X that was determined by theacceleration sensor BSH.

Furthermore, in the case of the third exemplary embodiment, thoseelements which are identical to those of the preceding exemplaryembodiments are provided with the same reference symbols so thatreference can be made to the disclosure in regard to the precedingexemplary embodiments.

In a fourth exemplary embodiment of the solution in accordance with theinvention which is illustrated in FIGS. 17 and 18, there is provided inthe intermediate piece 146 forming the section 60 of the supporting armand in a similar way to the second exemplary embodiment a break-through180 which passes through the section 60 of the supporting arm andextends in parallel with the vertical neutral reference surface NRFV andis bounded by an upper flange 182 and a lower flange 184 and in whichthere is arranged a sensor unit 190 which comprises a sensor carrier 192that is intersected in a central volume region 194 thereof by thevertical neutral reference surface NRFV in the same way as in the secondexemplary embodiment.

Hereby, the sensor carrier 192 carries strain sensors 206 and 208 whichare arranged on sensor carrier surfaces 202 and 204 and which, in thesame way as was the case in the second exemplary embodiment, are able tocapture the material tensile stresses MBS_(Z), MBS_(X) and MZS_(X)arising in the sensor carrier 192 by means of the elongations orcompressive distortions occurring in the sensor carrier 192 in theregion of the sensor carrier surfaces 102 and 104.

In this case, the sensor carrier 192 is likewise coupled directly to thesection 60 of the supporting arm in that the sensor carrier 192 is apart that is connected to the remaining section 60 of the supporting armin one-piece manner so that all of the reversible deformations in thesupporting arm region 60 are transmitted qualitatively to the sensorcarrier 192 and thus the same elongations and compressive distortionscan be captured qualitatively in the sensor carrier 192 by the strainsensors 202 and 204.

Thus for example, in the event of a static load imposed by the force FZ,this can be determined by the strain sensors 206, 208 whereby, in thecase of the device in accordance with the invention, the force FZrepresents a hitching-load of a trailer or a load carrying unit that isacting on the element 40 of the supporting arm 130′.

Due to the effect of the horizontal longitudinal force FX, the self-sameelongations arise everywhere in the section 60 of the supporting arm sothat the strain sensors 206, 208 all capture substantially the self-samematerial bending stresses MZS.

In particular in the case of the device in accordance with theinvention, a horizontal longitudinal force FX of this type represents atensile force which is acting on the element 40 when the motor vehicleis being driven along, whereby the mass of the trailer effective on theelement 40 or of the load carrying unit acting on the element 40 can bedetermined from this tensile force together with a knowledge of theacceleration.

In the fourth exemplary embodiment of the solution in accordance withthe invention in particular, an evaluating unit AU is provided on thesensor carrier 192 which captures the signals of the strain sensors 206,208 and determines therefrom the hitching-load FZ on the element 40 whenthe motor vehicle is stopped by consulting a table which associates thesignals of the strain sensors 206, 208 with a hitching-load for example,and thereafter determines the tensile force FX when it is being drivenalong by taking into consideration the measured hitching-load FZ, forexample, by consulting a table which links the values for thehitching-load and the signals of the strain sensors when it is beingdriven with a value for the tensile force.

Furthermore, an acceleration sensor BSH is additionally provided in theevaluating unit AU for capturing the acceleration in the horizontallongitudinal direction X so that the evaluating unit AU is also able todetermine the mass of a trailer engaging the element 40 or a loadcarrying unit held on the element 40.

In the fourth exemplary embodiment, those elements that are identical tothose of the preceding exemplary embodiments are provided with the samereference symbols so that reference can be made to the disclosure inregard to the preceding exemplary embodiments.

In a fifth exemplary embodiment which is illustrated in FIGS. 19 to 21,the supporting arm 130′ is, in principle, constructed in the same way aswas the case in the third exemplary embodiment although the sensor unit190′ together with the sensor carrier 192 is arranged on theintermediate piece 146 comprising the section 60 of the supporting armlaterally of the intermediate piece 146, but nevertheless in a mannersuch that the vertical neutral reference surface NRFV intersects thesensor carrier 192′ in a central volume region 194′ and hence thissensor carrier 192′ also comprises sensor carrier surfaces 202 and 204which are as arranged on oppositely located sides of the neutralreference surface NRFZ in the same way as in the second and fourthexemplary embodiment so that strain sensors 206 and 208 arranged onthese sensor carrier surfaces 202 and 204 likewise capture elongationsand compressive distortions of the sensor carrier 192′ of the same orderof magnitude.

Preferably thereby, the sensor carrier 192′ is firmly connected at theend regions 212 and 214 thereof to the intermediate piece 146 so thatthe sensor carrier 192 qualitatively experiences the same reversibledeformations as the intermediate piece 144 comprising the section 60 ofthe supporting arm in a similar manner to that of the second and fourthexemplary embodiment.

This solution has the advantage that no alteration of the supporting arm130′ itself such as by introducing the break-through 80 for example isnecessary but rather, the supporting arm 130′ can be formed such thatthe section 60 of the supporting arm itself is unchanged and, forexample, can merely be mounted on one side or else on opposite sides ofthe section 60 of the supporting arm of the sensor carrier 192′ in sucha way that the vertical neutral reference surface NRFV intersects acentral volume region 194′ thereof.

Consequently, the reversible deformations of the supporting arm 130′resulting from a vertical force FZ and a horizontal longitudinal forceFX are also detectable as elongations in the case of a sensor carrier192′ of this type having strain sensors 206 and 208 arranged on thesensor carrier surfaces 202 and 204.

Thus for example, in the event of a static loading by the force FZ, thiscan be determined by the strain sensors 206, 208, whereby in the case ofthe device in accordance with the invention the force FZ represents ahitching-load of a trailer or a load carrying unit that is acting on theelement 40 of the supporting arm 130.

Due to the effect of the horizontal longitudinal force FX, the sameelongations arise everywhere in the section 60 of the supporting arm sothat all the strain sensors 206, 208 capture substantially the self-samematerial bending stresses MZS.

In particular in the case of the device in accordance with theinvention, a horizontal longitudinal force FX of this type represents atensile force which is acting on the element 40 when the motor vehicleis being driven along, whereby the mass of the trailer acting on theelement 40 or of the load carrying unit acting on the element 40 can bedetermined from this tensile force together with knowledge of theacceleration.

In the fifth exemplary embodiment of the solution in accordance with theinvention in particular, there is provided on the sensor carrier 192′ anevaluating unit AU which captures the signals of the strain sensors 206,208 and determines therefrom the hitching-load FZ on the element 40 whenthe motor vehicle is at rest by, for example consulting a table whichassociates the signals of the strain sensors with a hitching-load, andthereafter, when it is being driven along, determines the tensile forceFX by taking into consideration the measured hitching-load FZ, likewisefor example, by consulting a table which links the values for thehitching-load and the signals of the strain sensors when it is beingdriven along with a value for the tensile force.

Furthermore, there is additionally provided in the evaluating unit AU anacceleration sensor BSH for capturing the acceleration in the horizontallongitudinal direction X so that the evaluating unit AU is also able todetermine the mass of a trailer engaging the element 40 or a loadcarrying unit held on the element 40.

In the fifth exemplary embodiment, those elements which are identical tothose of the preceding exemplary embodiments are provided with the samereference symbols so that reference can be made to the disclosure inregard to the preceding exemplary embodiments.

In a sixth exemplary embodiment that is illustrated in FIGS. 22 to 25,those elements that are identical with those of the preceding exemplaryembodiments are provided with the same reference symbols so thatreference can be made in regard to explanations of these elements to thefull content of the expositions in regard to the preceding exemplaryembodiments.

In the case of the sixth exemplary embodiment, the supporting arm 130″is again provided with a break-through 180″ in the region of theintermediate piece 146 that forms the section 60 of the supporting armwhich extends in parallel with the vertical neutral reference surfaceNRFV and passes through the entire section 60 of the supporting arm in adirection parallel to the vertical neutral reference surface NRFV,namely in a manner such that the vertical neutral reference surface NRFVruns through the break-through 180″ whilst the upper flange 182″ and thelower flange 184″ are effective to provide the requisite stability ofthe intermediate piece 146 on both sides of the break-through 180″.

Sensor units 190″ of which each comprises a sensor carrier 192″ areinserted into the break-through 180″ from both sides, whereby the sensorcarrier 192″ is likewise arranged in such a manner that a central volumeregion 194″ is cut through by the vertical neutral reference surfaceNRFV.

Furthermore, each of the sensor carriers 192″ is provided with sensorcarrier surfaces 202 and 204 which are arranged at substantially thesame distance on mutually opposite sides of the vertical neutralreference surface NRFV and are thus able to capture the reversibledeformations of the sensor carrier 192″.

A releasable connection of the sensor carrier 192″ to the section 60 ofthe supporting arm is produced for example by bolting end regions 112″and 114″ of the respective sensor carrier 192″ to the section 60 of thesupporting arm whereby, as is illustrated in FIG. 25, the sensorcarriers 192″ comprise positive-locking surfaces 232, 234 which areplaceable on corresponding seating surfaces 236, 238 in order toestablish a positive connection to the section 60 of the supporting armat the respective end regions 112″ and 114″ of the sensor carriers 192″.

Hereby, the positive-locking surfaces 232 and 234 and the seatingsurfaces 236 and 238 are arranged in such a way that the end regions112″ and 114″ of the sensor carriers 292″ are fixable to the section 60of the supporting arm by a bolted connection 242.

For example, the bolted connection 242 causes the end regions 212″ and114″ of the sensor carriers 192″ to be pressed into the recesses 116″and 118″ in a direction of insertion 244 which runs parallel to thevertical neutral reference surface NRFV for example, whereby the seatingsurfaces 236 and 238 are each inclined to the direction of insertion 244and run conically or V-shaped relative to each other.

Furthermore, the positive-locking surfaces 232 and 234 are similarlyinclined to the direction of insertion 244 and are oriented in a V-shaperelative to each other so that the bolted connection 242 creates amutually non-rotational positive connection between the recesses 116″,118″ and the respective end regions 112″ and 114″ in order to transmitthe reversible deformations of the section 60 of the supporting arm atleast qualitatively to the respective sensor carriers 192″.

In this exemplary embodiment, the sensor units 190″ are separatelyproducible units which, for example, can be replaced in the event ofdamage and which can also be employed with supporting arms 130″ ofdiffering shape.

In this exemplary embodiment, the sensor carrier 192″ consists of amaterial having the same coefficient of thermal expansion as thematerial of the section 60 of the supporting arm in order to avoidstresses in the sensor carrier 192″ with changes of temperature.

In particular, the sensor carrier 192″ is made of the same material asthe section 60 of the supporting arm.

The fact that in this exemplary embodiment two sensor carriers 192″ arearranged on mutually opposite sides but in particular, are offsetrelative to an outer contour of the section 60 of the supporting armmakes it possible to carry out redundant measurements on mutuallyopposite sides with the strain sensors 206 and 208 of these sensor units190″.

Moreover, in this exemplary embodiment, the sensor units 190″ arearranged on mutually opposite sides of the transverse neutral referencesurface NRFQ so that the possibility also exists of capturing reversibledeformations in the section 60 of the supporting arm that are producedby the horizontal transverse force FY by means of differing elongationscaptured by the one sensor unit 190″ with respect to the other sensorunit 190″.

Thus, for example, in the event of a static load imposed by the forceFZ, this can be determined by the strain sensors 206, 208 on the twosensor carriers 192″ whereby, in the case of the device in accordancewith the invention, the force FZ represents a hitching-load of a traileror a load carrying unit that is acting on the element 40 of thesupporting arm 30.

Thus, in a comparable manner, the respective strain sensors 206, 208 ofthe two sensor units 190″ that are spaced apart from one another arealso arranged on mutually opposite sides of the transverse neutralreference plane NRFQ and are arranged relative to a surface regionFB_(NRFQ) in such a way that the respective strain sensors 206, 208 ofthe two sensor units 190″ lie within the surface region FB_(NRFQ) in thecase of a vertical projection onto the transverse neutral referencesurface NRFQ, whereby the surface region FBN_(RFQ) extends in each ofthe directions of extent thereof lying in the surface region FB_(NRFQ)to an extent which corresponds maximally to 1.5 times the extent of thestrain sensors 206, 208 parallel to these directions.

In addition, a vertical projection of the strain sensors 206 and 208 ofeach of the sensor units 190″ also lies within the surface regionFB_(NRFQ).

Due to the arrangement of the strain sensors 206, 208 of the two sensorunits 190″ at approximately the same distance from the transverseneutral reference surface NRFQ, a transverse bending loading BQ likewiseengenders signals of opposed prefix sign but in the same order ofmagnitude and preferably of approximately the same size from therespective strain sensors 206, 208 of the two sensor units 190″.

The horizontal transverse force FY determined by the sensors 206, 208 ofthe two sensor units 190″, in particular in the device in accordancewith the invention, represents a transverse acceleration on the element40 which, for example, arises with rolling motions of the motor vehicleor of the motor vehicle with the trailer or with the load carrying unitwhen the motor vehicle is being driven along.

Due to the effect of the horizontal longitudinal force FX, the sameelongations occur everywhere in the section 60 of the supporting arm sothat all the strain sensors 206, 208 of the two sensor units 190″capture substantially the same material tensile stresses MZS_(X)combined with the material bending stresses MBS_(X) caused by the leverarm H1.

A horizontal longitudinal force FX of this type represents, inparticular in the case of the device in accordance with the invention, atensile force which acts on the element 40 when the motor vehicle isbeing driven along, whereby the mass of the trailer acting on theelement 40 or of the load carrying unit acting on the element 40 can bedetermined from this tensile force in the knowledge of the acceleration.

In the solution in accordance with the invention in particular, there isprovided on one of the sensor carriers 190″ an evaluating unit AU whichcaptures the signals of the strain sensors 206, 208 of the two sensorunits 190″ and determines therefrom the hitching-load FZ on the element40 when the motor vehicle is at a standstill, for example, by consultinga table which associates the signals of the strain sensors with ahitching-load and thereafter, when it is being driven along, determinesthe tensile force FX and if necessary the transverse force FY by takinginto consideration the measured hitching-load FZ, likewise for example,by consulting a table which links the values for the hitching-load andthe signals of the strain sensors 206, 208 with a value for the tensileforce when the vehicle is being driven along.

Moreover, an acceleration sensor BSH which captures the acceleration inthe horizontal longitudinal direction X is additionally provided in theevaluating unit AU so that the evaluating unit is AU is also able todetermine the mass of a trailer engaging the element 40 or of a loadcarrying unit held on the element 40.

1. A device for pulling a trailer and/or retaining a load carrying unit that is mountable at the rear end of a motor vehicle body, comprising: a supporting arm which is connected to the vehicle body by a first end region and is provided at a second end region with an element for attaching the trailer and/or for fixing the load carrying unit, and furthermore comprising sensors for capturing reversible deformations of the supporting arm caused by loads on the supporting arm, strain sensors which are affected by the reversible deformations thereof are assigned to the supporting arm section of the supporting arm, and, for capturing at least one selected bending load, at least one strain sensor is arranged on one side and at least one strain sensor is arranged on an opposite side of a surface region of a neutral reference surface which is assigned to the selected bending load and in that the strain sensors are each arranged at a distance from the surface region.
 2. A device in accordance with claim 1, wherein each bending load is assigned a neutral reference surface.
 3. A device in accordance with claim 1, wherein a vertical projection of the strain sensors that are arranged on mutually opposite sides of the neutral reference surface onto the surface region lies within the surface region.
 4. A device in accordance with claim 1, wherein, in each of the directions of extent thereof, the surface region exhibits an extent which is maximally double the extent of each of the strain sensors parallel to this direction of extent.
 5. A device in accordance with claim 1, wherein the strain sensors arranged on mutually opposite sides of the respective neutral reference surface are arranged at distances from the respective neutral reference surface which are such that the distance to the at least one strain sensor on one side of the surface region of the neutral reference surface lies within the range of 0.5 times up to 1.5 times the distance to the at least one strain sensor on the opposite side of the surface region.
 6. A device in accordance with claim 1, wherein the strain sensors are aligned approximately parallel with the surface region of the neutral reference surface.
 7. A device in accordance with claim 1, wherein the strain sensors are arranged on sensor carrier surfaces running approximately parallel to the surface region and are connected thereto.
 8. A device in accordance with claim 1, wherein the selected bending load is caused by a force on the element in the vertical direction and in that the neutral reference surface arising therefrom is a vertical neutral reference surface.
 9. A device in accordance with claim 1, wherein the strain sensors are arranged and aligned in such a manner that they capture a horizontal tensile load by a horizontal longitudinal force on the element.
 10. A device in accordance with claim 1, wherein the section of the supporting arm is fixed in such a manner that the neutral reference surface of this section of the supporting arm comprises a component in a horizontal longitudinal direction.
 11. A device in accordance with claim 10, wherein the neutral reference surface of this supporting section runs substantially parallel to the horizontal longitudinal direction.
 12. A device for pulling a trailer and/or retaining a load carrying unit that is mountable at the rear end of a motor vehicle body, comprising: a supporting arm which is connected to the vehicle body by a first end region and is provided at a second end region with an element for attaching the trailer and/or for fixing the load carrying unit, and furthermore comprising sensors for capturing reversible deformations of the supporting arm caused by loads on the supporting arm, a sensor unit comprises a sensor carrier which is provided on mutually opposite sides with sensor carrier surfaces upon which strain sensors are arranged and connected thereto, and the sensor carrier is connected to a deformable supporting section of the supporting arm in such a manner that the sensor carrier displays a reversible deformation behaviour which is qualitatively identical to the reversible deformation behaviour of the section of the supporting arm.
 13. A device in accordance with claim 12, wherein the sensor carrier is arranged relative to the section of the supporting arm in such a way that a neutral reference surface of the section of the supporting arm for capturing a selected bending load comprises a surface assigned to this bending load that intersects a volume region of the sensor carrier lying between the sensor carrier surfaces.
 14. A device in accordance with claim 13, wherein the neutral reference surface intersects a central volume region of the sensor carrier.
 15. A device in accordance with claim 13, wherein the sensor carrier extends along the neutral reference surface.
 16. A device in accordance with claim 12, wherein the sensor carrier surfaces are arranged on mutually opposite sides of a longitudinal central axis of the sensor carrier.
 17. A device in accordance with claim 12, wherein the mutually opposite sensor carrier surfaces are each disposed at distances from the neutral reference surface which differ from each other by a factor in the range of 0.5 to 1.5.
 18. A device in accordance with claim 12, wherein the sensor carrier has such a small effect upon the reversible deformation behaviour of the section of the supporting arm that the magnitudes of the reversible deformations of the section of the supporting arm which occur when the sensor carrier is present amount to at least 0.90 times the magnitudes of the reversible deformations of the section of the supporting arm without the sensor carrier.
 19. A device in accordance with claim 12, wherein the sensor carrier is connected in one-piece manner to the section of the supporting arm.
 20. A device in accordance with claim 12, wherein the sensor carrier is a component mounted on the section of the supporting arm.
 21. A device in accordance with claim 12, wherein the sensor carrier consists of a material having the same coefficient of thermal expansion as the section of the supporting arm to which it is connected.
 22. A device in accordance with claim 20, wherein the sensor carrier comprises mutually spaced end regions, and in that the sensor carrier surfaces for the strain sensors lie between the end regions.
 23. A device in accordance with claim 22, wherein only the end regions of the sensor carriers are held in seatings arranged in the section of the supporting arm which transmit the reversible deformations arising in the section of the supporting arm due to the loads to the sensor carrier.
 24. A device in accordance with claim 23, wherein the end regions engage in the seatings in the section of the supporting arm in which these end regions are fixed in positive-locking manner and which transmit the reversible deformations of the section of the supporting arm comprising the seatings and additionally extending between the seatings to the sensor carrier.
 25. A device in accordance with claim 24, wherein the seatings comprise seating surfaces which are effective on the end regions and have at least one component that extends in parallel with the respective neutral reference surface.
 26. A device in accordance with claim 24, wherein the end regions comprise positive-locking surfaces having at least one component which extends in parallel with the respective neutral reference surface.
 27. A device in accordance with claim 12, wherein the sensor carrier has at least one component, in particular the longitudinal central axis thereof which extends in a horizontal longitudinal direction.
 28. A device in accordance with claim 27, wherein the sensor carrier extends substantially parallel to the horizontal longitudinal direction.
 29. A device in accordance with claim 12, wherein the sensor carrier is arranged beside the section of the supporting arm such that it is offset in a direction parallel to the respective neutral reference plane.
 30. A device in accordance with claim 29, wherein the sensor carrier is arranged on a long side of the section of the supporting arm.
 31. A device in accordance with claim 12, wherein the section of the supporting arm comprises a recess and in that the sensor carrier is arranged so as to engage in the recess of the section of the supporting arm.
 32. A device in accordance with claim 12, wherein, as measured along the selected neutral reference surface, the section of the supporting arm is spaced from the first end region by a distance which lies in the range of 0.3 times up to 2 times the distance from the second end region.
 33. A device in accordance with claim 12, wherein a curved piece is provided between an intermediate region of the supporting arm comprising the section of the supporting arm and the first end region and/or the second end region of the supporting arm.
 34. A device in accordance with claim 12, wherein the section of the supporting arm lies in a central region between the first end region and the second end region of the supporting arm.
 35. A device in accordance with claim 1, wherein an evaluating unit is provided which evaluates the signals of the strain sensors.
 36. A device in accordance with claim 35, wherein the evaluating unit determines the force acting on the element in the vertical direction.
 37. A device in accordance with claim 35, wherein an evaluating unit determines a horizontal transverse force.
 38. A device in accordance with claim 35, wherein the evaluating unit determines a horizontal longitudinal force.
 39. A device in accordance with claim 35, wherein an acceleration sensor is assigned to the evaluating unit.
 40. A device in accordance with claim 39, wherein the acceleration sensor captures at least one acceleration in the horizontal longitudinal direction.
 41. A device in accordance with claim 1, wherein the supporting arm is a ball neck which, at its second end, carries an element in the form of a coupling ball that serves for attaching a trailer and/or fixing a load carrying unit.
 42. A device in accordance with claim 12, wherein the supporting arm is a ball neck which, at its second end, carries an element in the form of a coupling ball that serves for attaching a trailer and/or fixing a load carrying unit. 